Various parts in gas turbines are subject to high temperatures, and as a result are liable to degrade or disintegrate. One set of such parts is internal hot gas surfaces or walls. These surfaces can be cooled from the back side (cold side) to improve their lifetime. However, lifetime is still limited, and once failure starts to occur (for example a crack), then the part must soon be replaced, as the damage is liable to rapidly spread. This is particularly the case once any crack becomes big enough that significant cooling air is lost through the hole, reducing cooling effectiveness. As an example, an impingement cooled back side allows cracks or openings of a maximum area of the sum of all impingement holes feeding that area in order to remain functional.
It has therefore been appreciated that improvements can be made to provide more durable and better cooled hot gas surfaces.